Hydrofoil craft



May 30, 1967 c. HooK 3,322,089

HYDROFOIL CRAFT Filed June '7, 1965 5 Sheets-Sheet, l

May 30, C. HQOK HYDROFOIL CRAFT 3' Sheets-Sheet 2 Filed June 7, 1965 .W mu ff/ Hf@ @C5 m ,Y n f P N m M 7 MWH H Y c5 HYDROFOIL CRAFT Filed June 7, 1965 5 Sheets-Sheet if? @Wm/MM ,United States Patent O 3,322,089 HYDROFOIL CRAFT Christopher Hook, Hydron Design Centre, Yateley Hill, Yateley, England Filed June 7, 1965, Ser. No. 461,777 Claims priority, application Great Britain, June 11, 1964, 24,231/64; July 8. 1964, 28,046/64 Claims. (Cl. 114-665) This invention relates to hydrofoil craft and more particularly to such craft that use fully submerged foils wherein the lift is varied by changing the angle of incidence attack) of the foil relative to the water ow or line of ight.

Hydrofoil craft which travel over the water on hydrofoils connected to the hull by vertical struts are more vulnerable to floating debris such as logs of wood than are normal boats, and it is important to provide means whereby such floating debris cannot endanger the safety of the craft or passengers or cause any serious material damage.

With the fully submerged type of foil this danger is somewhat greater, and the need for foil safe provisions therefore more apparent. The reasons are basically:

1. Not having emerging foil tips that can be set at a larger angle of attack (as in those hydrofoil craft which use the emerging foil area method of control in altitude) there is nothing to stop a bad crash when air enters the low pressure area above the foil and the lift is lost.

2. In order to make air entry to the foils more diicut these are mounted at the bottom but to the front of the vertical struts attached to the hull. In this position they tend to hook on to any log of wood or other similar obstruction and its liberation is more diicult.

The invention accordingly consists in a variable-incidence hydrofoil assembly for a hydrofoil craft comprising a strut adapted to be attached to a hull of the craft for pivotal movement about an athwartships axis, means adapted to locate the strut in a generally vertical position and yieldably to restain it from movement from that posi tion, a hydrofoil pivotally mounted on the strut about an athwartships axis, a control rod passing down the strut, and means connecting the hydrofoil to the -control rod t0 vary the angular location thereof in relation to the strut and for releasing the hydrofoil from the control rod when the angle of incidence assumes an eiective negative value beyond a predetermined limited.

Preferably, the connecting and releasing means comprises gearing over a limited arc whereby the hydrofoil can be released from the control rod on movement outside the range covered by the arc.

Thus, on hitting a log or similar heavy object in the water the strut shall first swing rearwards through a small angle and from the athwartships pivot located near the top of the strut. The stmt is normally held in an upright position by the said pivot together with another member or strut attached to a point below the pivot and going rearwards to a point on the hull. This member can conveniently be a hydraulic piston or actuator which, on extension retracts the whole strut forward and upwards so that the foil comes out of the water. Rearwards of the upright position the strut will incline backwards so that the log tends to be pushed downwards and the hull to ride over the log. At this point a downward pressure will be exerted on the foil both by the log and by the water and when this force has reached a predetermined value the foil will assume the negative incidence and the whole foil shall turn over about its pivoted mounting thus allowing the log to pass and the strut to ride up over it.

Over the normal working range of incidences necessary to fly the boat the teeth will mesh, but when on swining back the log forces the foil to a much more negative angle than that required for ight the two gears will no longer be meshed together but will be free so that the foil can turn right over. This is accomplished by ending the teeth at that position and indeed only a small sector of teeth is required.

In order that this free sector shall not be used in normal ight, in which case the boat could turn over for lack of proper incidence control, it is best protected by suitable shear pin devices. Likewise the strut cannot depart from its normal upright position and incline rearwards before a shear pin has been broken by the exceptional drag given by the log.

The method has the advantage over other systems wherein the foil is attached by shear points to the hull that with this means the foil is not lost and can be brought back into mesh with the teeth after the strut has been retracted.

The invention further consists in a hydrofoil craft having a pair of hydrofoil assemblies according to the invention as set forth above mounted on the hull thereof.

The manufacture of large highly stressed hydrofoils in steel has presented hitherto almost insurmountable problems of manufacture.

The main diiculty is that the foil must have an ankle joint at or near its hydrodynamic centre if dicult forces are to be eliminated from the controls. It follows that for such a joint to be clean and well streamlined to avoid corrosion-producing cavitation at high speeds it must be well blended into the depth of the foil thickness and the corresponding or mating strut joint has similar very diiiicult requirements. Normally the centre of pressure of a foil falls at or very near the 25% chord point but in view of the angle of sweep it falls at about of the chord on the centre line where the foil starts to become thin. However, another requirement of cavitation avoidance requires the presence of a body of revolution along the centre line with the nose a short distance in advance of the apex of the two wings. It is inside this body that the hinge can be merged by blending the circular nose shape progressively to a square shape in the region of the pivot. However if the body has to be cast together with the foil there is no way of turning it on a lathe and machining the surfaces of the joint is made almost impossible in View of its diiicult location.

In a second aspect the invention accordingly consists in a variable-incidence hydrofoil for a hydrofoil craft, comprising a hydrodynamically streamlined central section generally in the form of a body of revolution, said central section at a rear portion thereof for pivoting the hydrofoil to a supporting strut and a recess therein, and a hydrofoil section having a projection entering the recess, the hydrofoil section and the central section being secured together.

The invention further consists in a hydrofoil assembly including such a foil, and in a hydrofoil craft having a pair of such assemblies.

The problems of safe failure for a hydrofoil drive mechanism of the two drive form is somewhat more complex than the corresponding problem for the variable incidence hydrofoils, because of the need to cater for the transmis sion of drive, for steering, for the retraction of the drive, and possibly for incidence variation on the tail foil.

In those struts which are used to transmit power to a propeller, generally known as Z-drives, it has been customary to exploit the special qualities of the cardan joint to both eliminate the torque reaction of the propeller from the steering gear and to allow fail safe and retraction. However all previous systems have certain limitations and some sacrice both the cardan and the tail foil when the fail safe is used. This represents a grave breakdown which in the ocean might be dangerous.

Two known types of hydrofoil craft have different advantages and drawbacks. One offers incidence correction to the tail foil by adjustment of the strut out of the ver- Y it will yield under a predetermined tical, but destroys its drive cardan joint on fail safe and retracts its foil completely but lacks fail safe.

It is a further object of the invention to provide a system in which all these requirements are met.

Accordingly in a third aspect, the invention consists in a drive and tail foil assembly for a hydrofoil craft, cornprising a main strut having a hydrofoil and a propeller mounted thereon and carrying an outboard drive mechanism for the said propeller, a secondary column including pintles rotatably supporting the main strutrabout a steering axis, an inboard drive shaft being driveably coupled to the outboard drive mechanism by a universal joint located on the said steering axis, the said secondary column being pivotally mounted in a bracket, about a fail safe pivot axis, the fail safe pivot axis being generally horizontal during the ight of the craft, yieldable means restraining the secondary column from pivoting about theV said fail safe pivot axis, the said bracket being pivotal about the axis of the inboard drive shaft to retract the assembly so that the foil and propeller are out of the water, and releasable means for holding the said assembly in operation position to prevent retraction.

The invention further consists in a hydrofoil craft including such a drive and tail foil assembly.

The invention will be further described with reference to the accompanying drawings, wherein:

FIGURE 1 is a side elevation of a preferred form of hydrofol craft according to the invention; Y

FIGURE 2 is a side elevation showing the fail safe action of a variable incidence foil;

FIGURE 3 is a side elevation of a hydrofoil;

FIGURE 4 is a plan view, partly in horizontal section, of the foil of FIGURE 3;

VFIGURE 5 is a section on the line V-V of FIGURE 4; and

FIGURE 6 is a section through the upper part of a drive and tail foil assembly in position at the stern of the craft.

FIGURE 1 shows a hydrofoil craft having a hull 1.V

Forward, variable incidence hydrofoils 2 are Vpivoted in vertical'struts 3. The struts are pivotal about an athwartships axis 4 and are yieldably located in the normal vertical position by a hydraulic piston cylinder unit 5 pivoted to the hull 1 and the strut 3.In addition a shear pin (not shown) may be incorporated to avoid the need for critical loading of the unit 5. Y

At the stern the craft has a further single vertical strut 7 housing a drive from an inboard motor to a propeller 8. The strut 7 also supports a xed hydrofoil 9.

FIGURE 2 shows diagrammatically what happens when one of the Lvariable incidence hydrofoils 2 strikesa floating obstruction such as a log 10. p

Itwill be understood that in the majority of cases the obstruction will be swept out of the way or broken or cut by the impact, but occasionally a bulky obstruction will get caught on the strut. In order to protect the strut and hydrofoil from damage, which could incapacitate the craft, the strut 3 is so mounted, as described above, that stress and pivot to the position shown dotted. The change of angle might be sufficient to dislodge the obstruction, but if not thefoil itself Y is also so mounted as to retract to the position shown dotted, to allow the obstruction to pass under the foil, upon being stressed above a predetermined limit. The manner in which this is achieved will be described with reference to FIGURES 3 to 5. It will be appreciated that such a movement of the foil will cause the craft to settle violently into the displacement mode of operation, but this is acceptable in View of the rarity of the occurrence. After resetting, however, the craft may normally recommence flight on the hydrofoils.

As shown in FIGURES 3 to 5, the hydrofoil'2 has a centre section 11 of rectangular form which merges into a tapered section 12 at the Vbottom of the strut 3. The sec- '.tion12 includes a lpair of forwardly extending ears 13 and does not retract the foil clear of the water. The other Y `of the foil in response 'to pilot operated and automatic,`

wave-compensating controls.

The rear teeth 17-preferably form a pinion so as to give a mechanical advantage and reduce the force necessary to move the foil by the control rod.

The normal extreme position of the link 18 are shown dotted in FIGURE 5. Upon the hydraulic control, and possibly a shear pin device, being overcomeby an excessive stress due to an obstruction so as to cause negative incidence of the foil above that indicated by the angle` 0 the Iteeth 16 and 17 are released and the foil is free to retract to the position shown dotted in FIGURE 2 to allow the obstruction to pass clear.

In order to simplify the manufacture of the hydrofoil, the central portion 31 is made separately, generally in the form of a body of revolution of hydro-dynamically streamlined form, which form is continued by the profile of the adjacent part of strut as seen in FIGURE 4. A recess 32 is machined in .the underside of the portionV 31. The hydrofoil itself is formed with a machined projection or iiat 33 matching the recess 32.

This enables the cross sectional area of the foil at the centre, its highest bending moment position, to be almost as large as the cross sectional area of the foil shape immediately adjacent to the centre portion 31 and the foil can be cast in a single piece with full strength. The final joint of foil to body of revolution may be bywelding or other fastening method. The foil being underneath, the lift tends toclose the joint.

FIGURE 6 shows in section the strut7 of FIGURE 1 and the details of its attachment to the hull 1. Y

The strut 7 carries a final drive shaft (not shown)rtoV the propeller 8, which -final drive shaft is connected to a vertical intermediate drive shaft 41. A horizontal outboard drive shaft 42 has bevel gears 43 and 44 rotatably mounted thereon and selectably connectable there to by dogrclutch shift sleeve 45. The bevel gears 43 and .4,4 are-in mesh ,withV a bevel gear 46 solid with shaft 41, to provide forward and reverse drive. Y

An inboard drive shaft 47 isV outboard driveV shaft 42 yby means of a universal joint 48. The axes of `the shafts'42 and 47 meet ata point 49. A secondary colum 50, parallel with the strut 7 is provided with upper and lower pintles 51 and 52 defining a steering axis 53 passing through the point 49. Upper and lower arms 54 and 55 support the strut] steerably on the pintles. The actual steering mechanis-mis conventional Vand is not shown. The column 50 is pivoted about an adjacent the surface 58, in a bracket portion 61. TogetherY with a main body portion 62, to which it is secured 4by a shear pin 63, the portion 61 forms a releasable L- shapedV bracket. To provide release, the portion `62 is mounted in a lathe-saddle type of slidefor vertical rnove-k Y ment in a thrust block 64. Mechanism, not shown, is

provided for moving the portion 62 downwards from and upwards to lthe position shown in FIGURE 6 to release and secure the secondary column 50, and hence the whole final drive and tail foil assembly.

upper' part of the j drivably connected to an engine and transmission (not shown) and also to the The thrust block 64 is itself mounted in a lathe-saddle type of slide `in a block 65 securely attached to the hull 1. A cam 66 on a camshaft 67 passing through the hull co-operates with a recess in the block 64 to provide fore and aft movement from the position illustrated in order to move the pintle 52 forward and aft to vary the incidence of the tail foil, for purposes of take off. The camshaft has a crank 68 thereon which is attached to a control mechanism under the pilots control.

The bracket 56 consists basically of a plate 71 parallel with the transom and of generally annular shape with a central aperture for the shaft 47 to pass through. An outer peripheral ange 72 is provided with gear teeth (not shown) for co-operation with a pinion (not shown) to rotate the bracket. The secondary column 50 is supported between two ears merging with the flange 72. A rubber or elastomer cushion block 73 is mounted on the plate 71 to limit movement of the column 50 about the fail safe axis.

The shaft 47 passes through an aperture in the transom and a sleeve 74, provided with supporting plates 75 and 76 is securely mounted in the transom so as to line and extend the aperture. A sleeve 77 is welded by its flange 78 into the aperture in the plate 71. This sleeve 77 is coaxial with the sleeve 74 and is rotatable thereon, being normally restrained against rotation by a removable pin 79. The shaft 47 is supported in the sleeve 77 by bearings 81 and 82 and seals 83 and 84 are retained by collars 85 and 86.

When retraction of the drive and tail foil assembly is required the body portion 62 and portion 61 are lowered in the slide block and the pin 79 is removed. The bracket 56 and drive assembly can then be rotated about the axis of the shaft 47 using the pinion and tooth arrangement described. To provide stability in the retracted position, a

coupling (not shown) may be provided to secure the end of the column 5G carrying the pintle 52 to the transom. The reverse procedure secures the assembly in normal operating position as illustrated.

On take off the block 64 is normally moved forward to increase the angle of incidence of the tail foil and is brought back to its normal position as illustrated once flight and speed have been established.

Normal drive thrust to the craft for the propeller is a forward thrust taken through the head 57 on the pintle 52 and transmitted through the thrust block 64. When the strut 7 strikes a floating obstruction, the obstruction is normally cut through or diverted without trouble. However occasionally a reverse thrust is applied to the strut 7 and this is applied by the lower arm 55 to the pintle 52. This causes the inclined surfaces 5S and 60 to engage and thus a downward thrust is exerted on the releasable bracket formed by portions 61 and 62 to overcome the restraining means holding the bracket in position. This bracket then drops to release the pintle and allow the assembly to pivot about the fail safe axis through about 457 until the upper end of column 5G strikes the cushion 73. In the alternative, the shear pin 63 will fail and release lower end of column 56. In this case the bracket portion 61 will be lost land must be replaced before the voyage can be continued.

A trigger is also provided to cut out the engine as soon as the load is shed by fail safe mechanism as described. This may conveniently be operated by any part that moves on fail safe coming into operation.

An advantage of the use of a horizontal slide for the block 64 is that it enables the thrust from the propeller, augmented by the mechanical advantages due to the lengths involved, to be measured for the purposes of research.

Various modifications may be made within the scope of the invention.

I claim:

1. A variable-incidence hydrofoil assembly for a hydrofoil craft comprising a strut adapted to be attached to a hull of the craft for pivotal movement about an athwartships axis, means adapted to locate the strut in a generally vertical position and yieldably to restrain it from movement `from that position, a hydrofoil pivotally mounted on the strut about an athwartships axis, a control rod passing down the strut, and means connecting the hydrofoil to the control rod to vary the angular location thereof in relation to the strut and for releasing the hydrofoil from the control rod when the angle of incidence assumes an eftective negative value beyond a predetermined limit.

2. A hydrofoil assembly as claimed in claim 1, wherein the connectino and releasing means comprises gearing over a limited arc whereby the hydrofoil can be released from the control rod on movement outside the range covered by the arc.

3. A hydrofoil assembly as claimed in claim 2, wherein the control rod is pivoted to a link pivoted in the strut about an axis parallel with the pivot axis of the hydrofoil and carrying a first set of gear teeth, a second set of gear teeth being located on the hydrofoil and adapted to mesh with the first set.

4. A hydrofoil assembly as claimed in claim 1, wherein the yieldable locating means is a hydraulic retracting piston and cylinder unit pivoted on the strut and pivotable on the hull, adapted to retract the strut forward and upward from the water, and to yield to allow the strut to move rearward and upward upon meeting an obstruction.

5. A hydrofoil assembly as claimed in claim 1, wherein the rearward retraction of the strut is normally prevented by a shear pin device.

6. A hydrofoil assembly as claimed in claim 1, wherein the movement of the hydrofoil to an effective negative angle is normally prevented by a shear pin device.

7. A hydrofoil craft including a hull, and a pair of variable-incidence hydrofoil assemblies mounted on the hull, each of the assemblies comprising a strut attached to the hull of the craft for pivotal movement about an athwartships axis, means adapted to locate the strut in a generally vertical position and yieldably to restrain it from movement from that position, a hydrofoil pivotally mounted on the strut about an athwartships axis, a control rod passing down the strut, and means connecting the hydrofoil to the control rod to vary the angular location thereof in relation to the strut and for releasing the hydrofoil from the control rod when the angle of incidence assumes an effective negative value beyond a predetermined limit.

8. A variable-incidence hydrofoil for a hydrofoil craft, comprising a hydrodynamically streamlined central section generally in the form of a body of revolution, said central section having means at a rear part thereof for pivoting the hydrofoil to a supporting strut and a recess therein, and a hydrofoil section having a projection entering the recess, the hydrofoil section and the central section being secured together.

9. A variable-incidence hydrofoil assembly for a hydrofoil craft, comprising a hydrofoil as claimed in claim 8, pivotally mounted on a strut by the means on the rear portion of the Central section, the adjacent portion of the said strut continuing generally the streamlined profile of the central section.

10. A hydrofoil craft having a hydrofoil assembly as claimed in claim 9, mounted at each side thereof.

References Cited UNITED STATES PATENTS 1,186,816 6/1916 Meacham 114-665 2,795,202 6/1957 Hook 114-665 2,906,228 9/1959 Wandel 114-665 3,209,714 lO/1965 Bowles 114-665 MILTON BUCHLER, Primary Examiner.

ANDREW H. FARRELL, Examiner. 

1. A VARIABLE-INCIDENCE HYDROFOIL ASSEMBLY FOR A HYDROFOIL CRAFT COMPRISING A STRUT ADAPTED TO BE ATTACHED TO A HULL OF THE CRAFT FOR PIVOTAL MOVEMENT ABOUT AN ATHWARTSHIPS AXIS, MEANS ADAPTED TO LOCATE THE STRUT IN A GENERALLY VERTICAL POSITION AND YIELDABLY TO RESTRAIN IT FROM MOVEMENT FROM THAT POSITION, A HYDROFOIL PIVOTALLY MOUNTED ON THE STRUT ABOUT AN ARTHWARTSHIPS AXIS, A CONTROL ROD PASSING DOWN THE STRUT, AND MEANS CONNECTING THE HYDROFOIL TO THE CONTROL ROD TO VARY THE ANGULAR LOCATION THEREOF IN RELATION TO THE STRUT AND FOR RELEASING THE HYDROFOIL FROM THE CONTROL ROD WHEN THE ANGLE OF INCIDENCE ASSUMES AN EFFECTIVE NEGATIVE VALUE BEYOND A PREDETERMINED LIMIT. 